Two-component polymeric materials such as reactive adhesives, paints, gasket materials and caulking materials comprise two separate components which react chemically with one another when intermixed. For example, two-component hot melt polymeric materials used in adhesive applications include a high volume polymeric material and a lower volume polymeric material such as a hardener. These types of hot melt adhesives, and other two-component polymeric materials, are dispensed from a system in which the two components are supplied from separate sources in a predetermined ratio to a dispensing device which then discharges the components into a mixer where the components are intermixed with one another before being emitted onto a substrate.
One problem with two-component dispensing systems of this type is that the two materials forming the two-component mixture begin to cure as soon as they come into contact with one another, and tend to collect on surfaces of both the dispenser and mixer, particularly when such components are dispensed intermittently. These cured materials can plug or at least constrict the flow of materials through the dispenser and mixer much like arteriosclerosis causes problems with constricting the flow of blood through the arteries and heart.
The problem of constriction of the flow paths through two-component dispensing systems has been addressed in U.S. patent application Ser. No. 07/640,043, mentioned above, in which a purging operation is performed to remove cured material from the system. In the practice of the method disclosed in Ser. No. 07/640,043, the supply of one of the two components to the dispenser and mixer is shut off, while the flow of the other component into the mixer portion of the system is permitted to continue. If hot melt polymeric materials are being dispensed through the system, for example, the high volume polymeric material may be used as the flushing material to perform the purging operation while the flow of the low volume polymeric material such as a liquid hardener is discontinued. The method disclosed in the Ser. No. 07/640,043 application has proven effective to purge the cured or partially cured mixture of the two components from the mixer portion of the system, but problems remain with removing the cured mixture from those portions of the dispenser where the two components come into contact with one another. Without an effective means for preventing or slowing the formation, and/or for removing such cured material from the dispenser, restrictions or clogs of the cured material can develop which eventually constrict and/or plug the passageways within the dispenser which emit the two components into the mixer.
Another aspect of two-component mixing and dispensing systems, particularly when operated intermittently, involves obtaining a clean, sharp cut off of the flow of the mixture emitted from the discharge outlet of the mixer portion of the system. In two-component dispensing systems of the type described above, valves are provided to control the supply of each component to the dispenser device, which then discharges the materials to the mixer. These valves may be located at the inlets to the dispensing device, which are remote from the discharge outlet of the mixer. This may result in the mixture leaking out of the mixer before the valves are reopened to resume the dispensing operation.